1. Field of the Invention
The present invention relates to an illuminator, more particularly to an illuminator being composed of a plurality of light source units that are radially arranged at a reference point of a base frame so as to improve luminosity of the illuminator.
2. Description of the Related Art
As light sources applied to a general lighting such as an indoor lighting, an incandescent lamp or a fluorescent lamp has been used so far; however, through the technical advancement of today's blue light-emitting diodes (the LEDs), the LEDs have come into use for light sources applied to, for example, ceiling lights or downlights. See Japanese Patent Application No. H10-21717 and WO 2007/023891.
As one of the examples, an illuminator 20 as shown in FIGS. 8 and 9 is mounted on an indoor ceiling, and is composed of: a circular light guide plate 22 including a circular inside end face 22a and a circular outside end face 22b; and a plurality of point light sources 24. The plurality of point light sources 24 are arranged along the inside end face 22a of the light guide plate 22. The light guide plate 22 is made of a transparent resin material such as polycarbonate resin, and is fabricated to have a certain thickness. An upper surface 22c (on the side of a ceiling surface 16) has, for example, dot patterns (not shown) working as a means to change the optical path of lights in which to be propagated in the light guide plate 22. Here, in FIG. 8A, the point light sources 24 are illustrated by a circular-band configuration; however, this actually means that the plurality of the point light sources are circularly arranged.
As shown in FIG. 9, a reflection plate 26 is arranged on the upper surface 22c of the light guide plate 22. A lower surface 22d (on the side of a floor surface) is a main surface formed as that the most parts of the light exit while incidence lights L have been propagating in the light guide plate 22. Further, a diffusion plate 28 is mounted on the lower surface 22d. Here, although the incidence lights L themselves exit with a certain angle width relative to a direction that orthogonally crosses the main surface 22d, with the optical diffusion effects provided by the diffusion plate 28, the incidence lights L are diffused further wide. The reflection plate 26 and the diffusion plate 28 are both circularly formed thereby being able to cover the light guide plate 22 and the point light source 24. In addition, the reflection plate 26 is normally either a diffuse-reflection material or a direct reflection material made of, for example, a white film or an evaporated silver film. On the other hand, any other materials may replace the diffusion plate 28 as long as the materials possess functions to diffuse the incidence lights L that exit from the lower surface 22d. Any types of a prism sheet may thus optionally replace the diffusion plate 28. Here, in the above illuminator, the plurality of point light sources 24 may be arranged along the outside end face 22b of the light guide plate 22.
Here, considering an illuminator using LEDs as a light source, since the luminous efficiency of the LEDs still needs further development, it is yet prerequisite to have a plurality of point light sources in order to satisfy properties (including luminosity) identical with conventional light sources such as a fluorescent lighting. In actual situations of the above conventional arts, the plurality of point light sources 24 are arranged along the inside end face 22a or the outside end face 22b of the light guide plate 22. However, due to the size of each LED or mounting pitches between each of the LEDs, the numbers of mountable LEDs should be determined based on the overall length of the inside end face 22a or the outside end face 22b. 